Method of ultrasonic pulse signaling



Dec. 7-, 1948. s. D.. EILENBERGER v2,455,475

. METHO oF ULTRAsoNIc PULSE SIGNALING Filed Sept.. 15, ,1943 A 2 Shee'ts-Sheet l v Mayu@ m. l A fr E v 3, '1 .fk )"2 my.

A'ITORN EY s. D. EILENBERGER METHOD OF ULTRASONIC PULSE SIGNALING Dec. 7, 1948.

2 Sheets-Sheet 2 Filed Sept. 15, 1943 FIG., 2 'mw.

, BYWWMI ATTORN EYS Patented Dec. 7, 1948 M'ETHD "0F ULTRASONIC PULSE SGNALING Stanley iD. rEilenbeigger, Kenosha,

by mesnenssignments, -to

Wiss fassigfnor, t(lhicagoiCoin Machine :Co., .a .conporation of Illinois AApplicationi-Septembor 15, 1943, LS'ev`ittl"l\lfo. 1502,528

This invention relates tofafmethodfofcommunication, more .particularly tto lultrasonic .signaling :for runder Lwater ruse '.Where the :communication lis secret iin .character and 'of .such a :nature .las .to -be `iliiieult or impossible for `,unauthorized :persons .to 4cari-.51.011,13 direction snding operations.

The present invention lis a :modified form of the inventions 'disclosed "by :niy zpat'ent ,applica- :tions entitled fRatio `signaling tsyst'emf YSerial lNumber 444,091, filed May 22, :1942,far1d H'g'hf speed 'transmission communication apparatus "Serial ,Numberffii, ifiled [August fla, 9.942, inow APatent No. :2;435g879, granted February 1194.8, `and reference should yloe made Vto .fthese lapnlica- :tions :for :a :better .understanding :of ;the-:present invention.

Briey, the invention consists zof a method whereby the atime frequiredito .transmit adnessage is vgreatlyzreduoed. 'This is iaccomplishedzby rst erecording :the message to be ftransmitted on .1a :magnetic sound track, :with itheisoundiiraok moving at the minimumisatisfactoryreoordhgnpeed, Aand then transmitting .this :recorded zmessage :at .high 'speed .in .such a manner that the .actual transmission ds :in the form of `an .ultrasonic ,-pulse, :thefduration ofiwliich is predetermined :At the receiving `station this process iis :reversed :to reF vcover the original signal.

It is old in l#the 1vart 'to :record :a .message `:on .a :moving `Vsound :track and to .fan-ch irecorded ymessage at -fa sound -rtr-ack zspeed consider'- a-bly ihighery than .the :recording fspeed, .to ioonserve transmission time. The .present '.invention :dislcloses .a method of transmitting iintelligence Awhereby the actual :transmission .consists of a. short :pulse cit-:ultrasonic .energy lor `a `series of lsuch 4short pulses, Where .reachisuoh .pulse has .a .denitefti-me ratiorto theitimexre'quired to irecord v.the original message and where reach .such :pulse .is sufficiently short fin .duration zthat `fdireotirm inding operations :couldbe :carried nutuonlywith the greatest diiculty fand with :elaborate equipment.

l For example, ,an original lmessage requiring 310 .seconds :to record :may the transmitaed in ;a ltotal timeperiod of .25 second, whichmouldibegatransmission/recording'fratio fof 40.31, vit being :understood that while -I have .used ithisiratio in factual practice, that :other ratios are also practical.

Among the numerous :objects :of this invention are:

First, to `provide la imethod offoommunieation -where the transmission :time :is .relatively fshort `as vcompared .to the ilength of :the .message vto be transmitted, so :that (direction inding ireadings 2 .on rsuon 'transmission are difficult or iimpossible to obtain.

Second to provide :a syste-m of A eommnninatio1:1 which sin itself .constitutes a )method fof fseoret .communication [hut which may be rcombined iwith and made a inart of any resisting :method :of :comF .munication this .combined .method foltering ithe further advantage ref additional seoreoy 1in faddi- 'tion :to lmaking it fdifloult or impossible rior ithe enemy to fobta-n @direction nding readings J.on .es uch ,tlansrnissions Third, Eto gprovide a :method fof (communication which will istill serve its [primary pmpose as :set ,ltorth .in the .first object ,above oven iwhere the .method :used :becomes known to the enemy, 4fas knowledge of :the Lmethod used .for such trans- .missions-.would not permitdireotion -nding read- .ings .tgo Jae :obtained l .fliourth, rtoprovidea methodof-.commnnication Where the seiective ,power .of the transmitter may be A@neatly :increased Abeyond the 'normal limitation ofplate dissipation `rating: of .the -nal ampli- .ifer tubes.

Fifth, 4to provide a method of .communication -as set `forth -in rthe iirst robiect above ,whereby ,longer .transmissions be carried v out as Lva A.series -of ultrasonic .pulses .spaced ras rdesired or necessary.

Sixth, to .provide ta .method :of combining nani or all cof .the-methods .above -in :a single system.

,It ynoderstood .that .one .basic -purpose of vthis invention :is zto `provide :a means :of vtransmittine fa message -zof :specigc iiength iin :a :relatively short period -of time, :as compa-red .to @the xtime required to record such lmessage and lthat lin ,the V .iorentiee tof 4the Lpresent invention, -the #transmission is :always 'carried out Joy .means of .this .relatively .-short pulse of ultrasonic-energy.

In the practice of the invention .herein odisclosed l properoonsideration must loe given to .cerf'tain .-eircnit com nonents .of yboth receiver and transmitter. E011 ipulposes 4`of example, .the .nonrnal voice `frennency rrange .may :be considered 'as `250 to 25,0013.. P..S.,.and -that.a ymessagecovering this range istobe recorded.oma magnetic sound `track ,within :a time :limitation tof l0 seconds, rand .that .such ,'10 second recorded message is `to .be transmitted .in .2-5 .second AThis would `be e recording/.transmission `ratio.t of 40 1. ,In -the example :given sabot/e, where )the .highest )frequency signal-was .takenas .250() gcycles, :the .highest x.ultra- .sonic ,frequency willbecome OILQOO cycles when `.reproduction of ,the recorded I-niessage .-is .carried .out ate times mormalsmrnd tracktspeed. This product of reproduction may tiren be @amplified 3 to produce an ultrasonic pulse, the duration of Which is .25 second, said pulse containing all of the information contained in the original signal.

The magnetic reproducing head must be able to properly reproduce at 100,000 cycles and the associated amplifiers must also function properly throughout this extended frequency range. The design of such ampliers is Well known to those skilled in the art, such ampliiiers being commonly used for various purposes, it being well known that such amplifiers may be designed to have a relatively flat gain characteristic throughout any desired frequency range or that such amplifiers may be designed to have a rising gain characteristic at the higher frequencies, if such rising gain characteristic is desirable.

The design of magnetic recording or reproducing heads to work efficiently at 100,000 cycles is also well known to those especially skilled in the art of magnetic recording. It is considered practical by those so skilled in the art of magnetic recording to record and reproduce by means of the magnetic process at frequencies considerably higher than 100,000 cycles per second, the maximum frequency recorded and reproduced being a function of the product of eifective pole piece dimensions and sound track speed. Theoretically, this recording/reproduction process may be carried out at any frequency where the product of effective pole piece dimension and sound track speed will not exceed one-half wave length of the highest frequency it is desired to record. The practical limit for such high frequency recording/reproduction is not definitely known, but it is definitely known that 100,000 cycles may be recorded and reproduced by the magnetic process.

The present invention does not deal with magnetic recording per se but is concerned with disclosing a method whereby the application of such a method may be so used as to produce a new and novel result. This disclosure is not confined to the use of any specifi-c recording medium and, with proper design of recording heads, the well known forms of magnetic tape or wire recording fmay be used. However, an improved magnetic recording or reproducing head design for use on a magnetizable cylindrical record is disclosed' by my patent applications, Magnetic pole piece, Serial Number 476,750, filed February 2, 1942, now Patent No. 2,361,753, granted October 31, 1944, and Magnetic recording and reproducing system, Serial Number 476,749, filed February 2, 1942, now Patent No. 2,361,752, granted October 31, 1944. These applications disclose a method of reducing the effective pole piece dimension to such a small value that a linear sound track speed of 6 inches per second is satisfactory for recording with voice frequencies up to 2500 C. P. S. With a recording/reproduction ratio of 40: 1 this would give a reproducing speed of 240 inches per second, which is equivalent to an R. P. M. speed of 1440 with a cylindrical record having a circumference of 10 inches. However, as previously mentioned,

this disclosure is not confined to the use of anyl particular form of magnetic recording.

For the purposes of this `appli-cation, the normal sound track speed is taken at 6 inches per second, it being understood that this speed is used only for purposes of example and that any speed giving satisfactory results may be used to record:

the original message. In the example given, reproduction is carried out at 40 times normal recording speed and the sound track reproducing speed is taken as 240 inches per second, for purv poses of example.

A further advantage of the present invention is that the power output may be greatly increased over the power output which would normally be possible for any given amplifier arrangement. All vacuum tubes designed for any form of amplifier service are rated in accordance with plate dissipation and this is a fundamental limit to the amount of plate input'power which may be applied to said vacuum tubes and is therefore a fundamental limit to the amount of output power available from said vacuum tubes. Other considerationsv are the internal insulation of the tube, which limits the maximum plate voltage which may be applied and the peak filament emission of the tube.

' It is well known that a definite time is required for any given tube to reach its rated plate dissipation. For example, with vacuum tubes of moderate power rating, approximately three seconds is required to reach the rated plate dissipation, if the full rated plate input is suddenly applied to the tube. For the special case where this tube was to be in service only 1/2 of this time or 1.5 seconds, the tube would reach its rated plate dissipation in 1.5 seconds if double the plate input was used for this time. Doubling the plate input for this time would not injure the tube, provided that the internal construction of the tube was such that increased voltage, per se, would not cause breakdown. A further limitation is the peak filament emission of the tube, but the actual peak lament emission of power tubes is greatly in excessof the rated continuous filament emission. For example, for certain moderate powered tubes rated at 500 milliamperes, continuous plate current, the peak filament emission is in excess 0f 5 amperes.

In the present invention, by way of example, the transmission time is limited to .25 second, and for-this special case the plate input to the final amplifier tubes may be increased to a value which will produce rated plate dissipation in the final amplifier tubes in .25 second. For certain graphite anode tubes in the medium power class, approximately l2 times the plate input power may be applied to the tubes for .25 second, as compared to the plate input power which could be applied continuously. This can be done without injury to=the tubes, provided internal construction is such thatbreakdown does not occur from excess voltage. Numerous such tubes are available on the open market, the construction being such that breakdown could not occur from excess voltage.

From the foregoing it is apparent that a relatively low power amplifier can provide a relatively high power signal, where such amplifier is used in accordance with the principles disclosed by this invention. For example, for the 40:1 transmission ratio cited above, a nal amplifier having a normal output rating of 10 watts of ultrasonic energy could produce approximately watts of ultrasonic energy, assuming the efciency to remain constant. As a matter of actual fact, the efficiency of most medium power tubes increases with plate input, so that for the special case herein cited, the efficiency somewhat improves over the rated efficiency. As previously stated, this high plate input will not produce actual damage in the tube. However, it is not known to what extent this high plate input pulse operation may shorten the overall life of the tube in terms of total hours of operation. Considering thespecial class of service, this factor is of minor importance, as only 1 hour of tube operation would be used in transmitting 40 hours of gettate message length; and 40E ncursmesfsage lengtlifor the special` case of ultrasonic signaling, ian'd'espe cially Afor military"signaling,- 'would'cever a con-` siderable periodof time, `ontheorderof many months. i l This invention will beV best understood froma consideration Aofthe follcwingdetailed descrip'-` tion in view of the accompanying drawings forming a part of the-specification; nevertheless, it :is understoodV that the *invention is not conned to the` disclosure, being susceptibleto-*such changes and modifications asdeineno material denari-` ture froml th'e salientfeatures--of"the invention as expressed in the appended" claims," *9 f Inthe drawings: j g Figure 1 shows in schematic form one arrangement of an ultrasonic `transmitter usedto produce a short-pulse or aseries"osh`ort pulsesf ultrasonic energy containing-the -intelligenceto be transmitted. Figure 2 showsinscheinatic form; onearrangee ment of a receiver "for usewitlr the transmitter ofFigure 1. Referring more particularly'to `Figure 1, Ais la source `of original signaLsuch as `a"inicrophcne, having output terminals@ connected toinput terminals d of amplifier B, in'serics with gain control 2. Amplier Bis anyconventional amplier which will amplify voi-ce frequenciesand provide a power output suitable1forrecordi`ng.` In ordi-` nary practice magnetic recording is carried out with a power considerably underl watt, sothat amplier' B may readilyV consist of'a one ortwo stage amplifier, depending 'infparton the "typev of signal supplied by Ullt A. "'Outputterminals t of amplifier B are connected'to common ground 28' and recording head 9, in series `with platere'- sistor l. Plate resistor `l"lin1`its the DLC.` current i'lowing through recording head 5l to the plate of the iinal amplifier tubeof ampliierB, Ithis D'. C.

current acting as a polarizing,current'formage netic recording head Si, polarity being so arranged that the current iiowing through recording head 9 is opposite in direction toltliefcurrent flowing in obliteration head i3', whichis directly across the source of plate voltage 33 ande/i in series with current limiting resistori Lwhich is in turn by-passedby condenser |25 i Magnetic obliterating head 'in is designedto produce magnetic saturation in `magnetidsound track D, the entire operation of clcgliteration` head lil, recording headI 9 and" magnetizable" sound track D being identicalfwith the magnetic recording process asconventionally used. 1 f Actual recordingis controlldby contacts I3 of relay it, which are in serieswith positiveplate voltage terminal 33, it being understood that-positive plate voltage terminal 33 and negativeplate voltage terminal 3ft, which are by-passed by con# denser 35i, are connected to a suitablefsource of D. C plate voltage. Relay M is controlled by timing unit E, which', Aforpurposes offexample, is shown as a synchronous motor driven timer having a cam 2li?, a cam extension 25, Vand a driving motor 2S. Driving motor`126 is energized by momentarily Vclosing' contacts 2l, allowing cam fit tc make onerevolution which` willifclnose#con-` tacts 23 for a predetermined'lengthoftinie; ac-` cording to the design of cam extension 25 and the speeclof driving motor 26." Motor `2t andrelayfl are energized from a `com mm sourceofvoltlage 29, which maybe any value desired. The entire arrangement ofA timing unit E andrela-y' Mi is such' that a deiinite recordinginterval isprovidd'. The* actualv` lengtnof the-"recordinginterval may; it desired; 1be` adjustable', but int any event `theanimar timeef sani interval is iimited by the actual spaceV available for recording on sound track D.' Sound track D may represent a magnetic' tape for Wire moving over drums 33 and' 36 in the direction indicated by arrow 37a, or sound trackDfm'aywell" represent the sound track on a cylindricalor disk record, as described in detail inf my patent application entitled Magnetic recording and'freproducing system, Serial Number 476,\749."' Driving-motor 31 is energized from a source of voltage 3| in series with resistor Sa, switch 3M being normally open during recording to provide the lower of two speeds available from driving motor 37, it beingV understood that while such an arrangement is practical for limited speed ratios that this arrangement is shown here only for reasons 'of simplicity and clarity in the drawings; it Y, being further understood that motors having gear change transmissions or other means ofichanging from one definite speed to a second denite speed may also be used without departing i from the principles disclosed by this invention.

i .waaier apsrsmate 144e the exampie given= a' lO'second message is recorded on' sound trackB, with driving motor 3i moving at a speed which will produce, forexample, a'lsound track speed of 6 inches per second,

magnetic soundtrack D, this l0 second recording intervalr being limited' by the operation of ,timingcircuitE;l At the expiration of lllseconds, contacts .i3 are restored to the normally open positionand plate voltage is removed from the iinal amplifier tubes in ampliiier B. The recording and obliteration process is now complete and the intelligence to be transmitted is recorded on sound track D. Thismessage may be preserved indefinitely on sound track D or it may be transmitted-immediately, as desired.

,Switch 3t'a is nowclosed, thus energizing motor 3l lat the highe'rfcf two speeds, to provide a magnetic sound track speed di) times greater than the reccrding'speed, which, for the example given', R. P. M., assuming that AdrH 35 and 35, or cylinder record 535-36, have circumference 'of l0 inches. Tiflis will provide a `reprodr ingspeed of 240 inches per second. The transmitter is now in a position to transmit, actual.Atransmission being. controlled by timing unit lgjmwhicn is simiiar to timing unit E previously described,-except .that cam extension 2d of cam iiis nowdesignedl tovclose contacts i8 for exactlyu secondgfor the example given, plus any desired tolerance, v 1 ,Th'ettraiiismission: cycle is initiated by closing Contact hthusenergizing timing motor 2li, timinglmo'toriiand relay le? being energized from a1 common sourceV of voltage Operation of relay iii `is controlled by timing contacts i8, and with theccperationaof relay ifinormally closed contacts. t6- areropened, thus removing the short circuit inparallel` with reproducing head l5. Reproducing head'. l5 is connected to input'terminals ii ci aniplierC, iii-series with gain control t;

incr 1C' being designed, according to the preseXarn-ple, toihave essentially flatgain throughout thefrequencyrange of. 10' k. c. to 10i) k. c., 'corresponds to a recording/transmission ratio` otLiO'zQlffori/oiee frequencies of 250 C. P. S; te=25ll0 Cil-P' S.. Output terminals "i" of amplifier arel directiy-connected to` an ultrasonic reproduci'ng device Iiilgrhere` shown asa piezo electric crystal mounted-between plates 38 and 3d, a sound projecting device 4l associated with plate ssffit being Luid-erstma that. tn-earrangement siioWnt-lis only -itni-Y purposes .ofi eraniple;Y and` that any form of ultrasonic reproducer may be used.

The arrangement shown is conventional, where 40 may well represent either a Rochelle salt crystal or a quartz crystal, both of these materials having the property of oscillating at an ultrasonic frequency when energy is applied to parallel plates between which said crystal is mounted. It is further understood that 4l may Well represent a directional device designed to focus the ultrasonic energy generated at diaphragm 39 by the vibration produced by piezo electric crystal 40 by the ultrasonic energy applied to terminals 38a and 39o, of the respective plates 38 and 39.

The transmission cycle is nowvcomplete, the total transmission having been carried out in .25 second, plus any desired tolerance, which may normally approximate an additional time of 5 milliseconds, to allow for operate time of relay l1, which may nominally be taken as 2 milliseconds. The power supplied to amplifier C may be raised above the normal rated input power for any given tubes used in amplifier C, the actual amount of such power increase beingv determined by the actual time of transmission and by the particular tubes used. For the example previously'given, the plate input power to amplifier C may be 12 times the normal rated input of the tubes used in amplifier C, which will result in a signal of approximately l2 times greater power being supplied to ultrasonic reproducer 40.

For the example previously given, amplifier C may be normally rated to provide watts output power and, by raising the plate input, may be used to provide 120 watts of output power for the time period of .25 second. This arrangement has the advantage of providing high output powers with relatively small amplifiers and although the power supply requirements are increased, the design of such power supply may be such that the weight or size represented does not exceed the design of a power supply used to provide lower plate power continuously, for the same reasons given in connection with amplifier C, i. e., filter choke coils designed to carry current for only .25

second may be designed with less core stack and smaller wire size than would be the case where such lter chokes are used continuously, as the limiting factor on wire size is the heat produced in the filter choke, and in the present assembly, the time element is suiciently short that the heat produced could be almost totally ignored. This is likewise true of other resistive and inductive components used in connection with amplier C and the associated power supply. f

For the example given, where the available power output is taken to be 120 watts with an ampliiier normally designed to carry 10 watts continuously, the improvement is not as great as would be the case where larger powers are involved, for example, with an amplifier using tubes normally rated to deliver 100` watts of energy, a full 1000 watts of energy may be delivered for the time of one transmission pulse, without increasing the weight or size of thev amplifier or the power supply used in connection with said ampliner. Such increased power would provide far more reliable communication and would also provide communication over greater distances, and under adverse conditions. While the foregoing has dealt with an original signal assumed to represent voice frequencies in the range of 250 to 2500 cycles, it is understood that other forms of signals may be used, such as, for example, telegraphy, facsimile, etc.

The operation of the transmitter has now been completely described, except that the function of unit X, which is shown connected to unit A, has been omitted. The function of lunit X is to supply a trigger frequency of some pre-determined value which in turn is used to energize the receiving station normally7 associated with the transmitter illustrated by Figure 1. The use of this trigger frequency is optional, depending in part on the particular design of the receiving station associated with the transmitter illustrated. For purposes of example, it may be assumed that unit X supplies a continuous frequency of 1250 C. P. S. which is recorded simultaneously with the intelligence represented by signal A. This is transmitted as a 50 k.,c. continuous signal which is used to trigger the receiver associated with the transmitter of Figure 1.

Referring now to Figure 2, which illustrates one form of receiver which may be used with the transmitter illustrated by Figure 1, the receiving piezo electric crystal is represented by 42, which may be Rochelle salt or quartz, 43 is the receiving diaphragm, 13a the directional receiving reflector and 43o the opposite contact plate, the entire assembly being similar to that used at the transmitter to produce the original ultrasonic pulse, which it is now desired to receive, the only difference being that in the case of the receiver the assembly need not be designed to handle any appreciable amount of power. It is understood that other forms of resonators sensitive to ultrasonic signals may also be used without departing from the principles disclosed by this invention. The voltage generated by piezo electric crystal 42 from the received ultrasonic vibrations is lconnected to input terminals 5|] of amplifier G, which has a frequency characteristic covering the range of 10 to 100 k. c. Output terminals 5I of amplifier G are connected to input terminals 52 of band pass filter B. P. which has a mid frequency of 50 k. c. Output terminals 5| of amplifier G are also connected to input terminals 44 of amplifier L, which has a frequency characteristic similar to amplifier G and is designed to further amplify the received signal before recording. The output terminals 53 of band pass lter B. P. are connected to the input terminals 54 of rectifier unit H, which may be a half or full wave rectifier unit of any type, such as vacuum tube, copper oxide, etc., output terminals 55 and 5B having D. C. polarity as indicated.

Trigger unit M comprises a gas discharge pentode 60 where suppressor grid 64 is normally biased negative in respect to cathode 66, so that a positive bias must be applied to control grid 65 in order to ionize vacuum tube 60. Sensitivity is controlled by potentiometer 69, the voltage across potentiometer 69 having a polarity as indicated. In the standby position the voltage 1U applied to suppressor grid 64 is suicient to maintain vacuum tube 60 in the de-ionized condition, for any given value of alternating current plate voltage supplied by transformer 12, which is in turn connected to a source of voltage 14, in series with switch 83. Rheostat 1I is designed to limit the current flowing through relay coil 62 and bypass condenser 91 is designed to hold relay 82 operated during the negative half of the plate Voltage cycle. This entire arrangement is shown here for purposes of example and represents only one form of trigger circuit which may be used with this receiver. In practice I have found that the arrangement shown is satisfactory.

In the standby position switch 83 is connected to contact 85, thus energizing transformer 12. B negative terminal 15 and B positive terminal 'i6 are lay-passed by condenser l|00 and-connected to a suitable source .of plate voltage. Switch unit l@ is Iinfcontact position 3U, .thus short circuiting series resistor 18, so that driving motor 182, which `isconnectedjto a source-of voltage l1, is operating 4.at the higher of two speeds, thus driving drums 96 and 95, or cylinder il--9.5, .and sound track N at a speed similar to but not necessarily identical tothe transmittingspeed"used at tl'i-eftransmitter, which vin the example given," was 240 inches per second, which is equivalent to 1440 R. P. M. for a drum circumference of inches. Recording and obliteration is held inoperative by normally open contact 63, until the k. c. trigger signal is received by ultrasonic resonator 42, ampliiied by amplifier G, passed by band pass filter B. P. and rectiied by rectifier H and the resultant D. C. voltage used to provide a positive trigger voltage on grid 65 of vacuum tube 60.

When this 50 k. c. trigger signal `is received, g

vacuum tube ionizes, thus operating relay 62 and closing contacts 03, which supplied obliteration voltage to obliteration head 51, in series with resistor 59, reverse polarity polarizing voltage to recording head 41 and plate voltageto the final stage in amplier L, in series with plate resistor 46.

The reception of the 50 k. c. triggering signal initiates the reception cycle, which will be completed in a total time slightly greater than .25 secz ond. When the trigger signal is cut off at the transmitter, at the end of the .25 second period,

`the positive bias voltage will be removed from grid E of vacuum tube 60, and the tube will deionize on the first negative half cycle of plate voltage, which will be in a maximum time of 1420 of a second if the supply voltage 'M is 60 cycles. This instantaneously stops the obliteration and recording process so that the received signal, which contains all of the original intelligence transmitted in the form of an ultrasonic frequency between the limits of 10 k. c. and 100 k. c., is now recorded on magnetic sound track N. Switch 19 is now moved to position 8i, so that driving motor 82 drives sound track N at the lower of two speeds, which, in the example given, Will be 6 inches per second. y

Switch unit 83 and switchunit 88 are mechanically linked by link Si? and this switch unit is now moved to position 8d and 89, thus opening the circuit to transformer 82 so that an additional received signal cannot obliterate the signal now recorded, thus initiating the reproduction cycle by connecting reproducing head 86 to the input terminals 92 of amplifier J ,in series with band rejection i-ilter B. R., which has a mid freduency :of 1250 cycles per second, and gain control 9i. Amplier J is designed to amplify voice frequencies in the range of 250 to 2500 cycles per second, the output terminals 93 of amplifier J being connected to input terminals 94 of reproducing unit K, which may be of any form desired, such as a loud speaker or head phones.

recorded signal maybe reproduced as many times as desired, after which switch units iid, and 'iii may be restored to the standby position, ready to receive and record additional The purpose of band rejection filter B. R. is to remove the 50 k. c. trigger signal '-.vhich has now been reduced to 1250 cycles, it being understood that other values of trigger signal frequencies may be used or that such triggering frequencies may be omitted altogether,

in which case part of the received signal is directly amplified and rectied in order to provide l0 1C. `voltage for triggering vacuum `tube fll. 'Ilie .advantage of using ra specific trigger freduency is that false operation is avoided, through pickup of underwater sounds, such as, for exam- Yple, propeller noise, it being further understood that the ,use `of-a trigger signal is optional.

In theexample given, switching is shown as a manual foperatiomfor reasons of clarity and simplicityzin the drawings, it being understood that fullilautomatic `operation may be utilized without departing from the principles disclosed by this invention. ,In A.the ,examples givenabove, Va complete signaling method has :been described where an original message was recorded within a 10 second time interval and transmitted as a single .25 second pulse of ultrasonic energy, thus giving a recording/transmission ratio of 40:1, it being understood that any other practical transmission vratio may be used. The maximum possible recording/transmission ratio is a function of equipment design, and it is understood that the recording/transmission ratios used by way of example are in no way limiting in scope as to minimum or maximum recording/transmission ratios which may be used in the practice of this invention.

-It is further understood that the maximum possible transmitter output power which may be obtained by the methods herein disclosed is a function of the vacuum tubes used, and of equipment design, and that the examples cited are in no way limiting in scope as to maximum possible transmitter output power which may be obtained by the methods disclosed by this invention.

The above examples are for the purpose of illustrating some of the methods and means by which the broad purposes of the invention may be carried out and are not to be deemed as restrictive in any manner. Other modifications and alternatives will occur to those skilled in the art without departing from the scope of the invention as dened by the following claims,

I claim:

1. rIhe method of signaling, which comp-rises the steps of recording within a limited time period the intelligence to be transmitted on a magnetic sound track moving at relatively slow recording speed, reproducing said recorded signal at relatively high magnetic sound track speed to produce a signal pulse of brief duration, converting said signal pulse into a pulse of ultrasonic energy, generating a control pulse, simultaneously transmitting said signal pulse and said control pulse to a receiver, causing said control pulse to render said receiver operative to record the received pulse on a magnetic sound track moving at a speed approximating said reproducing sound track speed at the transmitter, reproducing the pulse of energy so recorded and filtering the product of reproduction to recover the original v intelligence.

2. The method of signaling, which comprises the steps of simultaneously recording within a limited time period a control signal and the intelligence to be transmitted on a magnetic sound track moving at relatively slow recording speed, reproducing said recorded dual signal at relatively high magnetic sound track speed to produce a pulse of brief duration, converting said pulse into a pulse of ultrasonic energy, transmitting said pulse of ultrasonic energy to a receiver, selecting the part of said ultrasonic pulse representing said original control signal, and causing the part so selected to render said reeeiver operative to record the received pulse of ultrasonic energy, recording said pulse of ultrasonic pulse on a magnetic sound track moving at a speed approximating said reproducing sound track speed at the transmitter, reproducing the dual signal so recorded at a sound track speed approximating said recording sound track speed at the transmitter and lter-ing said reproduced dual signal to recover the original intelligence.

Y STANLEY D. EILENBERGER.

` REFERENCES CTlED The following references are of record in the le of this patent:

Number Number 

